U.S. Pat. No. 4,626,213, the disclosure of which is incorporated herein by reference, discloses a magnetic denture retaining unit comprising a ball and socket structure and a magnetizable keeper. The socket is adapted for incorporation into a denture. The ball is a permanently magnetized truncated sphere providing a flat base adapted for magnetic engagement with a flat face on the keeper. The keeper is adapted to be secured to a support member extending from the jaw of the wearer, such as a tooth or tooth piece or root, or an implant or shank replacing the tooth. The ball is mounted for oscillatory or swiveling movement within the socket so as to maintain the flat base of the magnetic sphere in full face-to-face contact with the flat face of the magnetizable keeper whenever an unsupported portion of the denture is stressed, either angularly or with a lateral displacing force, without substantial simultaneous stress being applied to the tooth piece or implant.
However, in some cases, the act of mastication or articulation of the jaw is of such magnitude that the denture is displaced laterally from the keeper to such extent that the magnetic grip of the magnet on the keeper is lost and the denture becomes disassociated from the keeper and free to move about in the mouth of the wearer. For use in such cases, it would be desirable to provide some means for preventing excessive lateral displacement of the magnet relative to the keeper so as to maintain the magnet in denture retaining relationship to the keeper.
U.S. Pat. No. 4,993,950 discloses, in FIG. 11, a magnet with a skirt that surrounds the upper portion of the keeper to prevent or limit lateral movement of the denture on the keeper. However, this arrangement requires the keeper to protrude from the keeper support and the patient's gum line, which is a source of irritation when the denture is not in place.